Coyolxauhqui is the Aztec Moon goddess. Her name means "Woman With Copper Bells on Her Cheeks", and when the moon rises full and red you can still see them.

Her mother, Coatlicue, became magically pregnant when a crown of feathers fell in Her lap. Believing Her family had been dishonoured, the angry Coyolxauhqui meant to kill Her; but the child Huitzilopochtli, whose name means "Hummingbird on the Left" (the south, i.e. the Sun), springing from the womb fully armored, defended Their mother and killed Coyolxauhqui instead. He cut off her head and flung it into the sky, where it became the Moon.
The combat between Coyolxauhqui the Moon and Huitzilopochtli the Sun represents the alternation of day and night.

From: Here
In Aztec mythology, Coyolxauhqui (Classical Nahuatl: Coyolxāuhqui [kojoɬˈʃaːʍki], "Face painted with Bells") was a daughter of Coatlicue and Mixcoatl and is the leader of the Centzon Huitznahuas, the star gods. Coyolxauhqui was a powerful magician and led her siblings in an attack on their mother, Coatlicue, because Coatlicue had become pregnant.

Attack on Coatlicue

The pregnancy of Coatlicue, the maternal Earth deity, made her other children embarrassed, including her oldest daughter, Coyolxauhqui. As she swept the temple, a few hummingbird feathers fell into her bosom. Coatlicue’s fetus, Huitzilopochtli, sprang from her womb in full war armor and killed Coyolxauhqui, along with her 400 brothers and sisters. He cut off her limbs, then tossed her head into the sky where it became the moon, so that his mother would be comforted in seeing her daughter in the sky every night.

Templo Mayor stone disk

A large shield-shaped stone relief reflecting this story was found at the base of the stairs of the Templo Mayor. On this disk, Coyolxauhqui is shown spread out on her side, with her head, arms and legs chopped away from her body. The orbiting full moon in the stone carving reflects her position as the moon goddess. She is distinguished by bells of eagle down in her hair, a bell symbol on her cheek, and an ear tab showing the Mexica year sign. As with images of her mother, she is shown with a skull tied to her belt. Scholars also believe that the decapitation and destruction of Coyolxauhqui is reflected in the pattern of warrior ritual sacrifice. First, captives’ hearts were cut out. Then they were decapitated and had their limbs chopped off. Finally, their bodies were cast from the temple to lie, perhaps, on the great Coyolxauhqui stone.

Coyolxauhqui in the present age

She is a major deity in Mesoamerica, living on in other areas in the approach to worship in all-night prayer vigils ongoing today in central Mexico, fully clothed in Christian adoration mixed with local ancestral remembrances and invocations.

Other associations

Coyolxauhqui’s celestial associations are not limited to the moon. Other scholars believe that she should be understood as the Goddess of the Milky Way, or be associated with patterns of stars associated with Huitzilopochtli.

From: Wiki
Name and Etymology:
Coyolxauhqui, "Bells of Gold"

Religion and Culture of Coyolxauhqui:
Aztec, Mesoamerica

Symbols, Iconography, and Art of Coyolxauhqui:

Coyolxauhqui is depicted with bells on her cheeks and surrounded by lunar symbols. Although thought of as a young goddess, sometimes her images show her as very old with sagging breasts. A massive statue of her unearthed in 1978 shows her with severed head and hands, just after Huitzilopochtli finished with her.

Coyolxauhqui was Goddess of:

Milky Way

Family Tree and Relationships of Coyolxauhqui:

Sister of Huitzilopochtli, Warrior God
Daughter of Coatlicue, Earth Goddess

Temples, Worship and Rituals of Coyolxauhqui:

When the Aztec sacrificed prisoners to Coyolxauhqui, they cut off their heads, cut out their hearts, and threw the bodies down Coyolxauhqui's temple. Thus the ritual heart sacrifices for which the Aztec became infamous for are recreations of the mythic story in which Huitzilopochtli kills his sister Coyolxauhqui.

Mythology and Legends of Coyolxauhqui:

Coyolxauhqui died when her brother, Huitzilopochtli, leapt from their mother's womb and killed all his siblings. Some legends say that she tried to warn her mother that her sons were about to kill her, other legends say that she was participating in the murder — even leading the way. Either way, she died and Huitzilopochtli threw her head up into the sky where it became the moon (so that their mother, Coatlicue, would be comforted by always seeing her in the sky) then her body down the hill of Coatepec.

Some scholars think that Coyolxauhqui may have represented a much earlier, female fertility cult in the region. Her death at the hands of her brother, Huitzilopochtli, would be then the mythical representation of a warrior cult assuming political and social control of the Aztec population. With Coyolxauhqui representing the moon and her brother, Huitzilopochtli, representing the sun, it's also possible that the conflict between them represents the continuous conflict between day and night.

Some scholars believe that the entire system of human sacrifice which underlies Aztec religion is, in some way, a recreation of this event because human sacrificial victims typically had their heads cut off an their bodies thrown down the steps of the temple.

From: Here

Coatlicue was the Earth, the mother of Coyolxauhqui, the Moon, and of Centzon Huiznahua, the "Four Hundred of the South" and another name for the Stars. One day, while she was sweeping her temple on top of Coatepec hill, the Earth was miraculously impregnated thanks to a little ball of feathers that floated down from the sky and that she tucked away next to her bosom. The Moon viewed the pregnancy of her mother as an affront and she instigated her brothers, the, Stars to kill her. Huitzilopochtli, the Sun, from her womb, warned the Earth of the danger and decided to defend his life and that of his mother. When the Moon and the Stars were on the point of killing her, the sun Huitzilopochtli was born, fully armed for war with a fire serpent called xiuhcoatl,with which he decapitated his treacherous sister, to then cast her down from the top of Coatepec hill. In her fall, the goddess was dismembered with each turn.

So the Moon dies every month, defeated by the Sun and cut in pieces. Coyolxauhqui and her dismemberment are the explanation for a celestial phenomenon, in which the moon dies and is born in phases, and so she was found at the foot of the stairway of the Huitzilopochtli temple at the Templo Mayor.

The relief shows the goddess decapitated, arms and legs dismembered, drops of blood oozing from her extremities and with the joints of her bones exposed. She is adorned with a two-headed serpent belt bearing a skull seen on her back. The two-headed serpent is repeated on the ties of her thighs and arms. The articulations and talons on her feet are adorned with masks composed of a profile face bearing fangs, the significance of which is still open to considerable conjecture. She wears her characteristic sandals, wristlets and anklets. Her torso, with flaccid breasts, is shown frontally, while her hips are given an unusual twist to be shown in profile along with her extremities. Her head displays a great feather headdress and her hair is adorned with circles. Composed of three geometric figures, her ear ornaments frame her face, which bears the most diagnostic element of her adornment: bells on her cheek, which is also the name of the Moon goddess. Finally, what appears to be her last breath issues from her half-open mouth.

The sculpture has a 3.25-meter average diameter. Weighing 8 tons, it is made of volcanic stone. It was found accidentally by Electricity Company workers who were installing underground cables at the corner of the streets of Guatemala and Argentina on February 21, 1978. This important discovery resulted in the archaeological excavations of the Templo Mayor Project, which until today continues under the direction of archaeologist Eduardo Matos Moctezuma.

From: here
"Golden Bells". The earth and moon-goddess of the Aztec. She is related to the four hundred star-deities Huitznauna, who are under her control. She possesses magical powers which with she can do great harm. When her mother Coatlicue became pregnant in what her children deemed unseemly circumstances, Coyolxauhqui and her 400 brothers and sisters sought to slay her. Immediately the sun-god Huitzilopochtli sprang fully armed from Coatlicue's womb and slew Coyalxauhqui and many of her kin.

According to one tradition, Huitzilopochtli tossed Coyalxauhqui's head into the sky where it became the moon. He hoped that his mother would find comfort at night by seeing the face of her daughter in the sky.

From: here

Other sites:

Short story thingy: go here.
Short summary
Interactive exhibit featuring her